The present invention is directed to a sealing gasket for a sealing station of a vacuum packaging machine. An example of such a vacuum packaging machine is disclosed in U.S. Pat. No. 5,271,207, which reference is incorporated by reference herein. At the sealing station, the upper and lower film layers forming the horizontal row or rows of filled vacuum-packages are heat-sealed together via an upper heating tool after the rectangular-shaped lower and upper tools of the sealing station have been brought against each other, and after a vacuum has been formed in the each package of the row of packages. The heating tool is lowered toward the upper surface of the outer rim of the lower tool and is supported thereagainst by a sealing gasket mounted by a perimetric groove formed in the upper surface of the outer rim of the lower tool.
The sealing gasket is usually rectangularly-shaped, defining an outer rim and a plurality of inner ribs or cross-members corresponding to the number of packages in a row being formed on the vacuum packaging machine. The sealing gasket serves to seal the sealing station during the vacuum-forming process, and has the additional function of bearing the entire load of the upper tool when the upper and lower tools are brought into abutting contact when a vacuum is created and when the packages of the row or rows are heat-sealed via the reciprocal heating tool associated with the upper tool. The heating tool has a plurality of heating elements corresponding to the shape and number of packages of a row or rows of packages being formed by the vacuum-packaging machine.
The material of which the entire sealing gasket is usually made is silicone rubber, in the approximate durometer-hardness range of about 65-75 Shore A, although polyurethane in the same hardness range is also used. This hardness is required since this sealing gasket, as explained above, must bear the entire load of the upper tool. However, there are a number of problems associated with making the sealing gasket of such hard material. Since the heating elements are not perfectly level, especially over time and use, it is common that some packages are formed that are not adequately sealed by the heating tool because of this unevenness or non-levelness of the heating elements, which not only require that these defective packages be discarded, but also require that time be spent by the operators of the machine in order to check for and discard the defective packages and remove the contents of these defective packages. Presently-used techniques to try to overcome this tendency of forming defective packages have been to increase the force, or load, of the heating tool against the lower tool of the sealing station. While this method produces some benefit, it is only partially successful and requires ever-greater force or load as the heating tool becomes ever-more uneven or non-level, which leads to a shorter life of the heating element and related equipment and the sealing gasket.
It is, therefore, the primary objective of the present invention to provide an improved sealing gasket for a vacuum-sealing station of a vacuum packaging machine, which improved sealing gasket overcomes the above-mentioned problems associated with the common occurrence of producing defective packages owing to the unevenness, or non-levelness, of the heating element.